I cringe every time I see this, because it almost always means there is a communication break down on both sides. I'm not saying for sure, I mean, I wasn't there, I don't know your mom, etc. But I have seen my teenage sister (10 years between us) treat my mother abruptly and dismissively, and then say that mom was the one who shut down the conversation. She won't explain and then complains that mom doesn't understand or won't listen. For my family, I could so easily see this conversation going as,

Mom: Why do you need these items?
Sister: Be-cause I want to make *dish*. ("Duh, Mom!" dripping with every word.)
Mom: But you can buy all of those things already made!
At this point my sister would sigh with annoyance, flusterdly wave a hand and say something that sort of explains the matter, but not really. Like, "It's not the same!" And then storm away with angst over no one understanding her. (Yeah, emo, I know.)

So I'm not saying this is how it went for you at all. I bring this up because I'm concerned about the bigger problem here. I hope, I think, that if you managed to have a sincere conversation with each other, she might be more understanding and willing to help. But, maybe I give her too much credit.

It's like you said though, she asked. She asked for the list. She asked questions. Maybe she is more willing to listen than she portrays.

And if not, I completely agree that you should ride to the store with her or find another way to the store. If she won't buy it, then the only other option is for you to do so.

you can give up on her listening...i would. take matters into your hands. bike, walk, to the store..and get your own food. it might seem silly but strollers work as excellent easy to manage grocery carts for long walks. been there done that.

as someone else asked, does your mom know youre dieting?

if so, maybe get her to come to a doctor with you. your height and weight put you in the obese category, so this isn't just a vanity diet. maybe if a doctor explains the risks associated with being obese, she'll get on board. if she doesn't, try to get other family members involved, maybe your dad?

my mom was the opposite and when i was 15 and weighed 110 would help me diet every time i wanted to. also not good.

this sounds like it may be a control issue at the core, assuming you're not giving her tons of attitude when you ask. you need to sit down and explain to her why you want and need to lose the weight.

My sister used a red wagon in that circumstance, and I have used a duffel bag with wheels.